Coated one-piece golf ball

ABSTRACT

The present invention provides a coated one-piece golf ball having excellent adhesion of a paint layer to a golf ball body and good appearance. The present invention relates to a coated one-piece golf ball comprising  
     a golf ball body formed by vulcanizing and press-molding rubber composition, and  
     a clear paint layer formed on the golf ball body, wherein the rubber composition comprises not less than 0.5 and less than 2.0 parts by weight of titanium oxide, based on 100 parts by weight of base rubber, and the clear paint comprises 0.1 to 2.0 parts by weight of fluorescent brightener, based on 100 parts by weight of resin solid content.

FIELD OF THE INVENTION

[0001] The present invention relates to a coated one-piece golf ball. More particularly, it relates to a coated one-piece golf ball having excellent adhesion of a paint layer to a golf ball body and good appearance.

BACKGROUND OF THE INVENTION

[0002] One-piece solid golf ball has been conventionally obtained by coating a white paint on the surface of a golf ball body, and then coating a clear paint on the white paint layer in order to impart brightly white appearance to the surface of the golf ball. However, since a color of the white paint and that of the golf ball body were different, there was problem that the white paint was removed when it was hit repeatedly, and the appearance of the golf ball was poor. Further, since one-piece golf ball has been mainly used at driving ranges for practicing golf, in which golf balls are hit repeatedly, there was problem that a piece of the paint layer having been removed at the time of hitting was adhered on a face of a golf club when the white paint is used for the golf ball.

[0003] In order to solve the problem, it was attempted to coat only a clear paint on the golf ball body without coating a white paint, but there was problem that whiteness of the appearance of the coated golf ball was degraded when compared with the golf ball coated with the white paint. In order to solve the problem, Japanese Patent Kokai Publication No. 51403/1995 proposes a one-piece golf ball having good white appearance with only a clear paint coating, which is obtained by formulating a proper amount of blue pigment and purple pigment into a rubber composition for the golf ball in addition to titanium oxide.

[0004] However, since the proposed one-piece golf ball contains a large amount of titanium oxide, there is problem its adhesion to the clear paint is degraded, although the mechanism has not been turned out. In addition, titanium oxide is relatively expensive and leads to cost-up of raw materials.

[0005] On the other hand, for a golf ball having a cover at a surface potion of a golf ball body, it is suggested to decrease an amount of titanium oxide in the cover composition (Japanese Patent Kokai Publication Nos. 70086/1989, 59879/1995 and the like). Decreasing the amount of titanium oxide in the cover without deteriorating its white appearance can be accomplished by containing light stabilizer, UV absorber and fluorescent brightener in clear paint as described in Japanese Patent Kokai Publication No. 70086/1989, or by containing fluorescent brightener and blue pigment in clear paint as described in Japanese Patent Kokai Publication No. 59879/1995.

[0006] The above techniques have not been yet applied to one-piece golf balls. In the above techniques, titanium oxide is present in the cover, but for a one-piece golf ball formed from only vulcanized rubber, a relatively large amount of titanium oxide should be formulated thereto because good white appearance is not obtained by a material such as a vulcanizing agent in the vulcanized rubber. This can be proven by the fact that there is a statement in Japanese Patent Kokai Publication No. 51403/1995 that a large amount of titanium oxide should be compounded and when the amount is smaller, golf ball appearance would be deteriorated.

OBJECTS OF THE INVENTION

[0007] A main object of the present invention is to provide a coated one-piece golf ball having both good adhesion of a paint layer to a golf ball body and good appearance.

[0008] According to the present invention, the object described above has been accomplished in a coated one-piece golf ball obtained by forming a clear paint layer on the surface of a golf ball body by reducing an amount of titanium oxide in rubber composition for the golf ball body to a specified range, and using a fluorescent brightener in a specified amount, thereby providing a coated golf ball having both good adhesion of a paint layer to a golf ball body and good appearance.

SUMMARY OF THE INVENTION

[0009] The present invention provides a coated one-piece golf ball comprising

[0010] a golf ball body formed by vulcanizing and press-molding rubber composition, and

[0011] a clear paint layer formed on the surface of the golf ball body,

[0012] wherein the rubber composition comprises not less than 0.5 and less than 2.0 parts by weight of titanium oxide, based on 100 parts by weight of base rubber, and the clear paint comprises 0.1 to 2.0 parts by weight of fluorescent brightener, based on 100 parts by weight of resin solid content.

[0013] The present inventors found that increase in an amount of the titanium oxide had a bad effect on adhesion of clear paint to the golf ball body and the adhesion was improved by reducing the amount of the titanium oxide to smaller than 2 parts by weight. However, whiteness is deteriorated, and the appearance is poor only by reducing the amount of the titanium oxide. It is considered to use a fluorescent brightener with the titanium oxide as described in the above conventional golf ball, but when it is compounded in the golf ball body, the technical effect accomplished by the presence of the fluorescent brightener is not sufficiently obtained, and good white appearance is not obtained. The present inventors also found that good white appearance is obtained by compounding the fluorescent brightener in the clear paint even if an increased amount of the titanium oxide is used. It is accomplished to effectively obtain good white appearance (without increasing the cost) by compounding the fluorescent brightener in the clear paint layer having light transmission properties even if the amount of the fluorescent brightener is small.

[0014] The term “golf ball body” as used herein refers to a golf ball itself before it is coated with paint, of which the surface portion has many depressions called “dimples”. The term “coated golf ball” as used herein refers to a golf ball having a paint layer obtained by coating a paint on the golf ball body.

DETAILED DESCRIPTION OF THE INVENTION

[0015] The one-piece golf ball of the present invention is formed from integrally molded article obtained by press-molding and vulcanizing a rubber composition. The rubber composition comprises a base rubber, a co-crosslinking agent, an organic peroxide, an inorganic filler, titanium oxide as a pigment and the like.

[0016] The base rubber may be one member or combination of two or more members selected from the group consisting of polybutadiene rubber (BR), ethylene-propylene-diene rubber (EPDM), polyisoprene rubber (IR), polybutyl rubber, natural rubber (NBR), styrene-butadiene rubber (SBR) and the like. The base rubber preferably contains the polybutadiene rubber as a main component, in a concrete way, the polybutadiene rubber is preferably contained in an amount of not less than 50% by weight of the base rubber. As the polybutadiene rubber, preferred is high-cis polybutadiene rubber containing a cis-1,4 bond of not less than 90%.

[0017] Examples of the co-crosslinking agents are not limited, but include α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms (e.g. acrylic acid, methacrylic acid, etc.), or mono- or di-valent metal salts, such as zinc or magnesium salts thereof. The preferred co-crosslinking agent is zinc acrylate because it imparts high rebound characteristics to the resulting golf ball. The amount of the co-crosslinking agent may be 15 to 40 parts by weight, preferably 18 to 38 parts by weight, based on 100 parts by weight of the base rubber. When the amount of the co-crosslinking agent is smaller than 15 parts by weight, the golf ball is too soft, and the deformation amount at the time of hitting is large, which degrades the adhesion of the clear paint. On the other hand, when the amount of the co-crosslinking agent is larger than 40 parts by weight, the golf ball is too hard, and the shot feel is poor.

[0018] Examples of the organic peroxides, which acs as a crosslinking agent or hardener, include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)-hexane, di-t-butyl peroxide and the like. The preferred organic peroxide is dicumyl peroxide. The amount of the organic peroxide is from 0.3 to 5.0 parts by weight, preferably 0.5 to 3.0 parts by weight, based on 100 parts by weight of the base rubber. When the amount of the organic peroxide is smaller than 0.3 parts by weight, the golf ball is too soft, and the rebound characteristics are degraded, which reduces the flight distance. On the other hand, when the amount of the organic peroxide is larger than 5.0 parts by weight, the golf ball is too hard, and the shot feel is poor.

[0019] Examples of the inorganic fillers include zinc oxide, silicon oxide, barium sulfate, calcium carbonate, aluminum silicate and mixtures thereof. The inorganic filler is used as reinforcing agents for improving the hardness or strength or a specific gravity (weight) adjuster. Preferred is zinc oxide, because it acts as vulcanization aid. The amount of the inorganic filler is from 15 to 35 parts by weight, preferably 20 to 30 parts by weight, based on 100 parts by weight of the base rubber. When the amount of the filler is larger than 35 parts by weight, the weight ratio of the rubber component is small, and the rebound characteristics are degraded. On the other hand, when the amount of the filler is smaller than 15 parts by weight, it is difficult to adjust the weight of the resulting golf ball, or the durability is poor.

[0020] In the one-piece golf ball of the present invention, it is required for the rubber composition for the golf ball body to comprise titanium oxide as a pigment in an amount of not less than 0.5 and less than 2.0 parts by weight, preferably 0.5 to 1.5 parts by weight, more preferably 0.5 to 1.3 parts by weight, based on 100 parts by weight of base rubber. When the amount of the titanium oxide is smaller than 0.5 parts by weight, whiteness of the golf ball is not sufficiently obtained, and the appearance is poor. On the other hand, when the amount is not less than 2.0 parts by weight, the adhesion to the clear paint layer is degraded.

[0021] The rubber composition for the one-piece golf ball body used in the present invention may optionally contain blue pigment in addition to the titanium oxide in order to impart further brightly whiteness. Examples of the blue pigments are not limited thereto, but include ultramarine blue, indanthrone blue, cobalt blue, fast sky blue, phthalocyanine blue, dark blue (Prussian blue) and the like.

[0022] The rubber composition for the one-piece golf ball body used in the present invention can contain other components, which have been conventionally used for preparing the one-piece solid golf balls, such as softener, antioxidant or peptizing agent in addition to the above components.

[0023] The one-piece golf ball body used in the present invention is obtained by mixing the rubber composition using a proper mixer such as a kneader and a mixing roll, followed by vulcanizing and press-molding the mixture in a mold. The vulcanization condition is not limited, but the vulcanization may be conducted at 130 to 240° C. and 2.9 to 11.8 MPa for 15 to 60 minutes. The vulcanization may be conducted in two or more stages of the temperature.

[0024] At the time of molding the golf ball body, many depressions called “dimples” are formed on the surface thereof. Furthermore, marking with a stamp may be optionally provided after molding. It is desired to properly grind the surface of the golf ball body before coating a clear paint in order to remove a release agent adhered to the surface during press molding. Therefore, the adhesion of the paint is improved.

[0025] The clear paint layer is then formed on the surface of the golf ball body. In the one-piece golf ball of the present invention, it is required for the clear paint to comprise fluorescent brightener in an amount of 0.1 to 2.0 parts by weight, preferably 0.15 to 1.5 parts by weight, more preferably 0.2 to 1.0 parts by weight, based on 100 parts by weight of resin solid content. When the amount of the fluorescent brightener is smaller than 0.1 parts by weight, whiteness of the golf ball is not sufficiently obtained, and the appearance is poor. On the other hand, when the amount is larger than 2.0 parts by weight, the technical effect accomplished by the presence of the fluorescent brightener is not further improved, or it is not preferable to increase the cost of the raw material.

[0026] For the clear paint used in the present invention, urethane resin, epoxy resin or acrylic resin can be used. Preferred is urethane resin-based paint. It is preferable to select the paint in consideration of the adhesion to the surface of the golf ball body. In a concrete way, the urethane resin, which includes active hydrogen containing compound such as polyester polyol, polyether polyol and the like as a main component and isocyanate compound as a curing agent, can be suitably used for the paint by reacting the main component with the curing agent. Examples of the isocyanate compounds include a modified 1,6-hexamethylene diisocyanate (burette-modified, trimethylolpropane-modified, trimerized), a modified tolylene diisocyanate and the like.

[0027] The fluorescent brightener compounded with the clear paint may be the same one that has been conventionally used for golf balls, and includes 2,5-bis(5-t-butyl-2-benzoxazolyl)thiophene (commercially available from Ciba Geigy AG under the trade name of “Ubitex OB”) and 7-(2h-naphthol-(1,2-d)-triazol-2-yl)-3-phenyl-cumarin (commercially available from Sunzos Co. under the trade name of “Leucopure EMG”) as a preferable examples, and includes biazoline derivative (commercially available from Mobay Chemical Corporation under the trade name of “Phorwhite K-2002”) and oxazoles (commercially available from Sumitomo Chemical Co., Ltd. under the trade name of “Whiteflure HCS”, “Whiteflure PCS” and “Whiteflure B”).

[0028] The clear paint used in the present invention may contains various additives and diluents, in addition to the above mentioned components. Examples of the additives are ultraviolet absorbers, antioxidants, light stabilizers and the like. The additives are present in an amount of 0.1 to 10 parts by weight, based on 100 parts by weight of the resin solid content of the paint.

[0029] The diluent used for the paint includes water; alcohols, such as isopropyl alcohol; aromatic hydrocarbons, such as toluene; aliphatic hydrocarbons, such as hexane; esters, such as ethyl acetate; ketones, such as methyl ethyl ketone; and the like. The diluent may be present in an amount of 5 to 50% by weight based on the solid content of the paint.

[0030] The clear paint is coated on the golf ball body by any art-known method, such as air gun coating, electrostatic coating and the like.

[0031] The weight of golf balls is limited to not more than 45.92 g in accordance with the regulations for large size golf balls, but the lower limit is not established. The one-piece golf ball of the present invention has a weight of 44.0 to 45.8 g, preferably 44.2 to 45.8 g. When the weight is smaller than 44.0 g, inertia of the golf ball on the fly is lost, and the golf ball stalls at the latter half flight period, which reduces the flight distance. On the other hand, when the weight is larger than 45.8 g, the shot feel is heavy and poor.

[0032] The one-piece golf ball of the present invention can have a diameter of 41.0 to 44.0 mm, but the diameter is preferably at least 42.67 mm in accordance with the regulations for large size golf balls, and the diameter is typically about 42.75 mm.

EXAMPLES

[0033] The following Examples and Comparative Examples further illustrate the present invention in detail but are not to be construed to limit the scope of the present invention.

[0034] Production of Golf Ball Body

[0035] The rubber composition having formulations shown in Tables 1 to 2 was mixed, and press-molded at 160° C. for 30 minutes in a mold to obtain a one-piece golf ball body having a diameter of 42.6 mm. The mold for molding the golf ball is composed of an upper mold and a lower mold having a semi-spherical cavity, and the cavity has dimples. TABLE 1 Golf ball composition A B C D E BR11 *1 100 100 100 100 100 Zinc oxide 23.5 23.5 23.5 20 23.5 Methacrylic acid 24 24 24 15 24 Zinc methacrylate — — — 10 — Dicumyl peroxide 0.6 0.6 0.6 2.5 0.6 Calcium carbonate 2 2 2 2 2 Titanium oxide 1.0 3.0 0.3 5.0 0.5 Blue pigment *2 0.04 0.04 0.04 0.05 0.04 Antioxidant *3 — — — 1 —

[0036] TABLE 2 Golf ball composition F G H I J BR11 *1 100 100 100 100 100 Zinc oxide 23.5 23.5 23.5 23.5 23.5 Methacrylic acid 24 24 24 24 24 Zinc methacrylate — — — — — Dicumyl peroxide 0.6 0.6 0.6 0.6 0.6 Calcium carbonate 2 2 2 2 2 Titanium oxide 1.0 1.5 2.0 1.3 1.0 Blue pigment *2 0.04 0.04 0.04 0.04 0.04 Antioxidant *3 — — — — — Fluorescent brightener *5 — — — — 0.2

[0037] The resulting golf ball body was pretreated by grinding the surface thereof. The clear paint compositions having the formulations shown in Table 3 (Examples) and Table 4 (Comparative Examples) were prepared. The paint was coated on the pretreated golf ball body by air gun coating, and dried and cured at 40° C. for 480 minutes to obtain a coated one-piece golf ball. With respect to the resulting coated golf ball, the adhesion and appearance of the paint layer were evaluated, and the results are shown in Table 3 (Examples) and Table 4 (Comparative Examples). The test methods are as follows.

[0038] (Test Methods)

[0039] (1) Adhesion

[0040] After coating the paint, the coated golf ball was left to stand under natural light for one month. After the coated golf ball was hit 100 times, the adhesion of the paint layer is evaluated by checkerboard peel test. The evaluation criteria are as follows.

[0041] evaluation criteria

[0042] ∘∘: Very good

[0043] ∘: Good

[0044] Δ: Fairly good

[0045] ×: Poor

[0046] (2) Appearance

[0047] The appearance of the coated golf ball was evaluated by 10 testers according to visual observation. The evaluation criteria are as follows.

[0048] evaluation criteria

[0049] ∘∘: No tester felt that the appearance of the golf ball is darkish.

[0050] ∘: From 1 to 2 out of 10 testers felt that the appearance of the golf ball is darkish.

[0051] Δ: From 3 to 5 out of 10 testers felt that the appearance of the golf ball is darkish.

[0052] ×: Not less than 6 out of 10 testers felt that the appearance of the golf ball is darkish.

[0053] (Test Results) TABLE 3 Example No. 1 2 3 4 5 6 7 Golf ball composition A A A E F G I (Clear paint composition) (parts by weight) Urethane resin *4 100 100 100 100 100 100 100 Fluorescent 0.2 0.5 1.0 0.2 0.2 0.2 0.2 brightener *5 Antioxidant *6 — — — — — — — (Test item) Adhesion ∘∘ ∘∘ ∘∘ ∘∘ ∘∘ ∘ ∘∘ Appearance ∘∘ ∘∘ ∘∘ ∘∘ ∘∘ ∘∘ ∘∘

[0054] TABLE 4 Comparative Example No. 1 2 3 4 5 6 7 Golf ball composition A B B C D H J (Clear paint composition) (parts by weight) Urethane resin *4 100 100 100 100 100 100 100 Fluorescent — 0.2 0.2 0.2 0.2 0.2 — brightener *5 Antioxidant *6 — — 1 — — — — (Test item) Adhesion ∘∘ x Δ ∘∘ x Δ ∘∘ Appearance x ∘∘ ∘∘ x ∘∘ ∘∘ Δ

[0055] As is apparent from the results of Tables 3 to 4, the one-piece solid golf balls of the present invention of Examples 1 to 7, when compared with those of Comparative Examples 1 to 7, have excellent adhesion of a paint and good appearance.

[0056] On the other hand, in the golf ball of Comparative Example 1, since the clear paint composition has no fluorescent brightener, the adhesion of the paint layer is excellent, but the appearance of the coated golf ball is poor. In the golf ball of Comparative Example 2, since the amount of the titanium oxide is large, the appearance is good, but the adhesion is poor. In the golf ball of Comparative Example 3, the adhesion is slightly improved by further adding the antioxidant to the paint of Comparative Example 2, but is not sufficiently obtained.

[0057] In the golf ball of Comparative Example 4, since the amount of the titanium oxide is small, the adhesion is excellent, but the whiteness is degraded, and the appearance is poor. In the golf ball of Comparative Example 5, since the antioxidant is used but the amount of the titanium oxide is large in the golf ball body, the appearance is excellent, but the adhesion is poor. In the golf ball of Comparative Example 6, since the amount of the titanium oxide is slightly large, the appearance is excellent, but the adhesion is slightly poor. In the golf ball of Comparative Example 7, since the amount of the titanium oxide is within the scope of the present invention, the adhesion is excellent, but the appearance is poor because the fluorescent brightener is present in the golf ball body, which is not in the paint. 

What is claimed is:
 1. A coated one-piece golf ball comprising a golf ball body formed by vulcanizing and press-molding rubber composition, and a clear paint layer formed on the golf ball body, wherein the rubber composition comprises not less than 0.5 and less than 2.0 parts by weight of titanium oxide, based on 100 parts by weight of base rubber, and the clear paint comprises 0.1 to 2.0 parts by weight of fluorescent brightener, based on 100 parts by weight of resin solid content.
 2. The coated one-piece golf ball according to claim 1, wherein the rubber composition comprises 0.5 to 1.5 parts by weight of titanium oxide. 